Electric-arc furnace



July 1 1924.

W. S. HADAWAY, JR

ELECTRIC ARC FURNACE Filed Dec. 10 1921 BY a INVEN TOR.

ATTORNEY.

Patented July 1,1924.

PATENT OFFICE.

WILLIAM S. H ADAWAY, JR, .0! NE'W'ROCHELLE, NEW YORK.

' ELECTRIC-ARC FURNACE Application filed December 10, 1921. Serial 170.521,333.

To all whom it may concern:

Be it known that I, WILLIAM S. HADA- WAY, Jr., a. citizen of the UnitedStates,

and a residentof New Rochelle, county of Westchester, and State of NewYork, have invented certain new and useful Improvements in Electric-ArcFurnaces, of which the following is a specification.

This invention relates to electric arc "furnaces, and more particularlyto such furnaces employing electrodes arranged to form an arc inproximity to a quantity of metal or the like to be heat treated.

Broadly stated it is an object of the present invention to provide anelectric arc furnace in which the efficiency of operation is greatlyimprovedby supplying a gaseous material directly to the arc.

Another object relates to the improvement of means for producing heatfor the treatment of metals requiring high degrees of heat withsubstantially no reaction or interference with the chemical constituentschange in the amount of carbon in a steel:

makes a greatly amplified change in the characteristics thereof, andthus the production of certain high grade steels, requiring' definite,critical proportions of carbon, is uncertain, and production schedulesrelating-thereto erratic.

In'its broader aspects, therefore, this invention is intended to reducecost and to overcome these difiiculties, and in furtherance of theseobjects various other important features are provided, which will appearfrom the following description taken in connection with the accompanyingdrawing, in which- Figure 1 shows a sectional elevation of a furnace;

'Figure 2 shows an enlarged sectional view of a portion of theapparatus; and

Figure 3 shows a section taken on the line 3-3 of Fig. 2.

Like reference characters refer to like parts in the several figures ofthe drawing.

For the purpose of showing more or less diagrammatically an apparatusembodying the invention, there is shown in the drawing a retort 10comprising a frame work 11 and a crucible 12 supported therein. Theframework 11 is constructed of metal plates suitably secured together.The crucible is made of a refractory material in the form of a bowlhaving an outlet which may be sealed by a detachable plug 13 also ofrefractory material. The upper surface of the furnace comprises a coverplate 14, also of refractory material, having a substantially centrallydisposed orifice for the re-' ception of a heater sleeve 15. The sleeve15 has a peripheral shoulder or flange 16 for positioning the sleeveupon the plate 14,. 7 and is preferably .formed of refractory materialcapable of withstanding very high temperatures. The lower extremity of'thesleeve 15 is open. The upper end of the sleeve 15 is closed by acover plate 17 made of refractory material and resting on an internalshoulder in the sleeve 15 and is re? enforced by a second plate 18. Theplate 18 is made ofa material which is an insulator of electricity, andwhich is capable of withstanding the degree of heat necessary.

A plurality of electrodes such as 20, 21 extend through slots in theplates 17, 18 the supports therefor being secured to the insulatingplate 18, in any desired manner. Each of these supports (Figure 2)comprises a yoke or bridge 22 for pivotally supporting upon trunnionbearings the respective electrode and its carriage 23 (Figure 3). Thusthe electrodes maybe rocked 0r tilted into and out of contact with eachother. Each of the yokes 22has an extension 24 with an upright toothedsegment 25, and the corresponding electrode carriage 23 has an arm 26movable in proximity to the segment 25. The free end of each arm- 26 isshaped in the form of a handle and suitable latching means 27 may beprovided for maintaining the electrode in a given position when desired.It 15 understood however that any suitable form 'of i or maintainingmeans, automatic,

manual or semi-automatic, may be employed for these purposes.

, The electrode supports and carriage are preferably made of nickelchromium or other suitable material.

The electrodes 20, 2l are made of a fulgarite such as oxide of magnesia,which is a conductor of electricity only when hot. They are made hollowin the form of tubes, the upper extremity of each being provided with asuitable binding post 30. Each electrode is mounted or clamped on thecarriage 23 in any suitable manner and a transverse passage 31 leadsthrough the wall of the electrode, one flange of the carriage member 23and through a stufling box' 32, connecting to a supply 33 for supplyinga suitable gas or vapor to the electrode. The binding posts each maycomprise a split collar of electrically conducting material fitted overthe upper end of the respective electrode, and fastened by means of asuitable set screw. Leading from the electrodes is a correspondingplurality of conductors connected to a source of current 34. The source34 may supply either direct or alternating current and as shown a singlephase alternating current is supplied; it is understood however that twoor three phase current may be employed, the number of conductors andelectrodes being then increased to four and three each respectively.

The supply 33. is connected to a main passage 35 leading to one of theelectrodesupports for supplying active medium thereto. A bypasstherefrom (see Fig. 1) leads to one part of a valve 36. A second part ofthe valve is. connected by means of a passage 37 to another of theelectrode supports, andserves to supply or to withdraw active mediumtherefrom depending upon the position of the valve 36. A third part ofthe valve 36 is connected by means of a passage 38to the source 33.

In the interior of the bowl 12 is placed a suitable quantity of material40 which is to be heat treated. When molten, the material may be removedby removin the plug 13 and tilting'the frame 11, the e being providedfor that purpose suitable trunnion bearings in the sides thereofsupported on upright brackets such as 41.

In operation, assuming that the source 34 is active, the electrodes arebrought into contact at their lowerends. On account of the highresistance of the electrodes when cold little'or no current flows. Thevalve 36 is set in the position shown in Figurel.

A supply of hot gas or vapor, such as superheated steam for example, isnow supplied through the passage 31 and the interior passage of each ofthe electrodes to the lower extremities thereof. The heat of the vaporis imparted to the electrodes, whose or crevices in the device.

resistance is reduced thereby, and current flows;

The electrodes are now separated, drawing an arc which produces anintense heat. A peculiar action now takes place, the theoreticalexplanation of which is in some doubt on account of obvious-difiicultiesof observation; but it is thought that the action may be that the oxideof magnesia of which. the electrodes are formed is decomposed, andalmost immediately recombines, so that there is substantially no real orpermanent combustion thereof. While in its decomposed state, however, itforins, in combination with the vapor emitted by the electrode ends, agaseous conducting path for th -current, so that a greatly extended arccan be formed with constant voltage and current factors.

The heat is imparted to the material 40 by radiation and reflection.Temperatures approximating. 5000 F. can be produced by such an arc,which is ample to raise the temperature of the material being treated todesired degrees.

'The heat transmitted by conduction through the electrodes 20, 21'totheir respective supports is imparted, to the incoming stream of vapor.The vapor, although hot, is at a temperature considerably below themelting point of nickel chromium or other material of which the supportsare made, and serves to limit the rise of temperature therein andprevent damage thereto. Thus it will be seen that the vapor performs athree-fold purpose: it heats the electrodes to make them conductors ofelectricity; it provides a path of electric conductivity for the currentin the arc; and after the arc has been started, the vapor limits therise of temperature of the electrode supports.

During the early period of the operation, the vapor after serving-itspurpose, or the residue of the vapor, escapes throughv leaks 1 Later thevalve 36 may be shifted to interconnect passages 37 and 38, thuspermitting circulation of the vapor in through one electrode and outloss. Furthermore, the lack of combustion,

imparts stability to the are not found with carbon arcs, the electrodesof which necessarily are continually consumed, thus varying the arc, andrequiring continualoperation of the regulating devices, and emitting anundesirable material in the-furnace.

When it is desired to remove contents of the crucible the source ofcurrent 34 and the supply of vapor are discontinued. The material 40 maythen be emptied out, and the. apparatus made -ready for subsequent use.7

electrodes.

Illustrativesapparatus has been described but itis ex-presly understoodthat the scope of the invention is not to be limited thereby,

reference being had to the appended claims vapor longitudinally throughthe electrodes.

3. An electric arc device comprising hols low electrodes of a materialwhich is a nonconductor of electricity when cold, and means for passinga hot vapor longitudinally through the electrodes.

4. An electric arc device comprising hol.

low electrodes of an oxide ,of magnesia, and. means for passing a hotvapor through said 5. An electric arc device comprising hol lowelectrodes of an oxide of magnesia, and a single means for conducting amedium to each of the electrodes for initially raising the temperaturethereof and for providing a gaseous ath for conducting electricity throuh t e arc.

6. electric arc device comprising means for introducing a flow of vaporfor providing a gaseous path of conductivity for the are.

7. An electric arc device comprising a plurality of. electrodes andmeans for introducing a flow of vaporfor providing a gaseous path ofconductivity for the arc.

8. An electric arc device comprising a plurality of hollow electrodesand means for introducing a flow of vapor through the electrodes forproviding a gaseous path of conductivity for electricity.

9. An electric arc device comprising a plurality of hollow electrodesand supports therefor, and means for introducing a flow of vapor throughthe supports and the electrodes to the are.

10. The method of maintaining an are which consists of supplying a flowof vapor and a current of electricity to the arc.

11. The method 'of initiating and maintaining an electric are whichconsists .of supplying a potential of electricity, supplying a hot vaporto initiate conduction of electricity and to form a gaseous path at theare for the electric current. i

- 12. The method of operating an electric are which consists of passinga vapor to the arc in such "manner as to cool the ends of the electrodesspaced from the arc ends, and imparting the heat of the electrodes tothe incoming vapor as it approaches the arc.

13. An electric furnace comprising electrodes composed of an oxide ofmagnesia.

14. An electric furnace comprisin hollow electrodes, means for supplyinge ectric means for energy thereto, and means for passing a vapor throughthe. electrodes. 7

15. An electric furnace comprising ho low electrodes of a material whichis a nonconductor of electricity when cold, and means for passing a hotgaseous medium through the electrodes.

16. An electric furnace comprising hol low electrodes of an oxide ofmagnesia, and passing a hot' vapor through said electrodes.

17. An electric furnace comprising hollow electrodes of an oxide ofmagnesia, and a single means for conductin a medium to each of theelectrodes for initially raising the temperature thereof and forproviding a gaseous path for conducting electricity through the arc.

18. An electric furnace, comprising means forintroducing a vapor forproviding a gaseous path of conductivity for the arc.

19. An electric furnace comprising a plurality of electrodes and meansfor introducing a vapor for providing a gaseous path of conductivity forthe are.

20., An electric arc comprising a casing forming a substantially closedspace, and electrodes protruding into the closed space, said electrodesbeing non-conductors of electricity at ordinary temperatures andconductors of electricity when hot.

21. An electric, arc furnace comprising a structure vforming asubstantially closed space, and electrodes which are non-conductors ofelectricity at ordinary temperatures and conductors of electricity whenhot, said electrodes being positioned to protrude into the closed space,and means for heating the electrodes.

22. An electric arc comprising a structure forming a substantiallyenclosed space, and electrodes protruding into the enclosed space, saidelectrodes being nonconductors of electricity at ordinary temperaturesand conductors of electricity when hot, and means for conducting aheating medium to said electrodes for'raising their temperature to apoint where they become conductors.

23. Any electric arcdevice comprising a furnace havin an enclosed space,and electrodes protru ing into the space and formed of a material whichdecomposes and recombines in the arc. 24. The method of initiatingandgmaintaining an electric are which consists of supplying a potentialof electricity, supplying WILLIAM s. HADAWAY,

